git-gui: fallback right pane to packed widgets with Tk 8.4
Since
918dbf58, git-gui crashes if started with Tk 8.4. The reason is that
tk < 8.5 does not support -stretch option for panedwindow.
Without the option it's not possible to properly expand the right half -
the commit area is expanded, while desired behavior is to expand the diff
area. So the whole feature should be disabled with Tk
version less than 8.5.
Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>